The present invention relates to a container closure and to a method for producing a liner material for use as a part of a container closure.
U.S. Pat. No. 3,335,897 of Anthony J. Castro discloses a container closure having a plastic material foamed in situ in a venting orifice. Gases may move through the foamed material and through the orifice but liquids are blocked due to the hydrophobic nature of the foamed material. The prior art is lacking in a method of providing foamed plastics material having the right combination of liquid blocking and gas permeable properties.